This invention pertains to color reproduction, in particular to color reproduction by a six-color ink jet printer.
Inkjet printers are being increasingly used for proofing and short-run production (e.g. fine art reproduction, textile). For example, in the textile area inkjet printers are being utilized for short xe2x80x9cpre-productionxe2x80x9d runs, which short runs are not cost effective for typical higher volume rotary screen printers due to the time and expense in cutting screens.
As such it is desirable to have the output of the inkjet printer be faithful to the original in all light, to all observers. In the particularly case of short xe2x80x9cpre-productionxe2x80x9d runs, it is highly desirable that the output of the inkjet printer be as identical as possible in appearance to output from a rotary screen printer, regardless of observation conditions.
Color matching/conversion systems correlating the outputs of various types of devices are known. See U.S. Pat. No. 5,579,031, which is incorporated by reference herein for all purposes as if fully set forth. In one aspect of this disclosure, color values are obtained for two devices, such as two different printers, and used to generate an adapter that correlates the outputs of the two printers so that images with substantially identical colors, when viewed under standard conditions, can be printed on either. The color values for the two printers are generated from data obtained via colorimetric measurements.
It is well known that four-color printing systems are highly metameric compared with objects undergoing graphic reproduction. It has been found that the calorimetric analysis as described in U.S. Pat. No. 5,579,031 is insufficient to minimize the metamerism inherent in normal four-color printing.
Six-color printers have the potential to reduce metamerism by providing a better spectral match, but the computation in such systems is substantially more complicated.
Previously, ink sets with more than four colors have been employed with the goal of gamut expansion, not metamerism minimization. The present invention provides a method to fully utilize the spectral gamut of a six-color printer to minimize metameric matches while maintaining high colorimetric accuracy.
In accordance with the present invention, there is provided a method of printing a reproduced image with an output printer with six-color output, wherein the reproduced printed image is a spectral and colorimetric match of a target image as would be printed with a target printer or other target color device, and wherein the target printer and the output printer are different, comprising the steps of:
(1) building a six-color spectral printer model of the six-color output printer based on spectral measurements of the output of the six-color output printer;
(2) obtaining a color spectrum of the target color device based on spectral measurements of the output of the target color device;
(3) fitting the color spectrum of the target printer to the spectral model of the output printer;
(4) mapping the target color device to the output printer based on the fitting, and
(5) printing the second image on the output printer based on the mapping.
The output printer is preferably an ink jet printer. The target color device can be an inkjet printer, a dye sublimation/diffusion device, slide printers, a rotary screen printer, a CRT, flat panel displays, and other electronic displays.
The six-colors of the output printer are preferably cyan, magenta, yellow, black, orange and green (CMYKOG). Each of the six colors can be present as full strength or some combination of full and/or partial strength to assist in color gamut expansion, for example, cyan and light cyan, and magenta and light magenta (CcMmYKOG).
The term xe2x80x9ca spectral and calorimetric match of a target image as would be printed with a target printerxe2x80x9d is intended to be descriptive of an improved overall color match as opposed to just a calorimetric match. There is provided an optimized, but not necessarily perfect, match of spectral and colorimetric properties. In other words, the present process is designed for metamerism minimization in a typically highly metameric environment, so that the xe2x80x9creproducedxe2x80x9d image more closely resembles, in all aspects and under all viewing conditions, the original image as it would appear when printed with a target printer.
For example, it is a goal of the present invention to be able to print an image with a six-color ink jet printer so that it has a substantially identical appearance with a minimum of metamerisms as compared to the same image when printed with a typical rotary screen printer. This would allow cost effective short run production of images using digital printing, which would otherwise be cost prohibitive in rotary screen printing due to the time and expense in cutting screens.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description. It is to be appreciated that certain features of the invention that are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. In addition, references in the singular may also include the plural (for example, xe2x80x9caxe2x80x9d and xe2x80x9canxe2x80x9d may refer to one, or one or more) unless the context specifically states otherwise.